Ab-initio calculation of elastic constants of oxide and nitride crystals

The goal of this thesis is to develop a reliable and stable scheme to investigate the complete set of independent elastic constants and structural properties for various crystals in different lattice structures using density functional theory and a combined computational and theoretical approach. A theoretical formalism to calculate the elastic constants for cubic and hexagonal single crystals from first principle calculations is described. The geometry optimization was performed using the Vienna Ab-initio Simulation Package (VASP) with both local density approximation (LDA) and generalized gradient approximation (GGA) based on the total energy calculation. All independent elastic constants as well as the bulk modulus, Young's modulus, Shear modulus and Poisson's ratio for a series of oxide and nitride crystals which have cubic and hexagonal structure under different k-point mesh were calculated. A comparison between our result and series of experimental data as well as results from other calculations was performed.